With the increase in concern about environmental issues, the demands on automobiles for better fuel economy have been increasing in recent years. Better fuel economy is also being required of rubber compositions used for automotive tires. For example, rubber compositions containing a conjugated diene polymer (e.g., polybutadiene, butadiene-styrene copolymer) and a filler (e.g., carbon black, silica) are used for automotive tires.
Patent Literature 1 proposes an example of a method for improving the fuel economy; this method uses a diene rubber (modified rubber) that is modified by an organosilicon compound containing an amino group and an alkoxy group. Although the use of a modified rubber increases reaction efficiency between silica and rubber (polymer) to improve the fuel economy, it tends to increase the Mooney viscosity so that the processability tends to deteriorate. Thus, good fuel economy and good processability cannot be achieved simultaneously. Furthermore, the use of a modified rubber may lead to excessively tight bond between silica and rubber so that the rubber strength and the abrasion resistance may decrease.
Additionally, as rubber compositions for automobile tires need to be excellent in wet-grip performance and handling stability in view of safety, a technique is desired which achieves a balanced improvement in these properties as well as fuel economy, processability, rubber strength and abrasion resistance at high levels.